DO NOT MERGE ANYWHERE Use protobuf for trunk_staging

This change causes trunk_staging to use the protobuf implementation of
build flagging, and makes it fail if using legacy build flag
processing.

Bug: 328495189
Test: manual, TH
Change-Id: I663a23bea7fc0af6bfb3e6e0a80c7636cfc3a2ad
Merged-In: I663a23bea7fc0af6bfb3e6e0a80c7636cfc3a2ad
3 files changed